There are known methods of preparing tableted reagents that contains chlorine or iodine compounds and are intended for in field clarification of natural water. However, such reagents only sanitize water, and the treated water has an offensive odour and taste, which causes resistance to use it. Production of such tablets is complex and the tablets have short storage life.
A known tableted composition is commercially available under Chlor-Floc (trademark), and method of its application [Reference 3 Powers E. M., Hernandez C., Boutros S. N., Harper B. G. Biocidal Efficacy of a Flocculating Emergency Water Purification Tablet. Appl Environ Microbiol. 1994 July: 60 (7), pp. 2316-2323]. These tablets combine disinfection with clarification by sedimentation-filtration. The chemical constituents of the tablet are similar to many that have been used by municipal water treatment plants.
US Patent [Reference 4 U.S. Pat. No. 5,681,475, B01D 15/00, Issued: Oct. 28, 1997] describes a composition in unit dosage form (powder, granular or tablet) for batchwise water purification comprising: (a) an organochlorine compound serving as a disinfectant-sanitizing agent (sodium dichloro-s-triazinetrione or sodium dichloroisocyanurate, and a combination thereof); (b) a solid inorganic metal salt (aluminum sulfate); (c) a solid alkali which in the presence of an acid serves as a dispersion-buffer agent (sodium bicarbonate); (d) a solid primary flocculant (sodium carboxymethylcellulose); (e) a solid secondary flocculant (high molecular weight polyacrylamide polymer); (f) a long fibre cellulose; and (g) a bulk ion exchange absorbent (zeolite).
Russian Federation patent [Reference 5 Russian Federation Patent No 2278827, C2 M CO2F1/50 (2006.01) A61L 2/23 (2006.01) C02F 103/04 (2006.01), Issued: Jun. 27, 2006] claims a composition of the following compounds: sodium salt dihydrate of dichloroiso cyanuric acid in the amount of 3-250 parts by mass, succinic acid in the amount of 5-100 parts by mass and sodium chloride in the amount of 3-50 parts by mass; it also additionally contains sodium bicarbonate in the amount of 10-250 parts by mass. Another complex composition is claimed in another Russian Federation patent [Reference 6 Russian Federation Patent No 2 255 898, C17 C01F7/00, C01F7/58. Issued: Jul. 10, 2005] as well.
Disadvantages of both compositions are complex formulation thereof, difficulties in preparation, and short storage life.
A more useful technical solution is the method claimed by patents in US and Canada [Reference 1, Canadian Patent No 1 186 967, C02F1/56 (2006.01), C02F1/54 (2006.01), C02F1/52 (2006.01), Issued: May 14, 1985, and Reference 2 U.S. Pat. No. 5,023,012, C02F1/52 (20060101). Issued: Jun. 11, 1991]. The composition comprises: (a) 40-60% (by mass) aluminum sulphate as a coagulant for rapidly coagulating solid impurities dispersed in the water to form primary flocs; (b) 15-25% (by mass) sodium bicarbonate for alkalization as a coagulant promoter; (c) 2-25% (by mass) bentonite as a clay (acts as centres of sedimentation in low turbidity water); (d) 0.5-3% (by mass) sodium dichloroisocyanurate as a first micro-biocide agent; (e) 1-3% (by mass) carboxymethylcellulose for aggregating the primary flocs into larger secondary flocs; (f) 1-3% (by mass) synthetic silicon hydroxide compound; (g) 0.02-0.15% (by mass) polyacrylamide as a secondary colloid; and (h) 4% (by mass) halazone (dichlorosulfamylbenzoic acid) as a second micro-biocide agent.
The basic disadvantages of this composition are the very complex formulation, low stability of some components, insufficient aluminum sulphate effectiveness as coagulant under low temperature of treated water, and the high price of reagents. Surprisingly the present invention makes use of the well-known ability of titanium dioxide particles to adsorb and hold on its surface gaseous chlorine. Usually manufacturers of titanium dioxide, using the chloride method of production, apply significant effort to remove the chlorine. Another engineering solution for dechlorination of titanium dioxide described [Reference 9 Russian Federation Patent No 2 042 628, 6 C 01 G 23/08. Issued: 27 Aug. 1995]. The method is carried out at a mist-laden hot air flow fluidized bed and results in chlorine content decrease. Titanium dioxide obtained by this method has a low chlorine content (less than 0.2%) and is not an effective disinfectant.
Contrary to these systems, the present invention makes use of the ability of titanium dioxide to adsorb chlorine and then to release it in aqueous media, as well as the technology of surface treatment.